With the development of electrical vehicle (EV), EV chargers are designed and central charging stations are constructed globally for electrical vehicles. PCT application WO2012/119300 A1 discloses an EV charger unit. According to FIG. 1 of WO2012/119300 A1, standard IGBT bridges are adopted in EV charger unit for AC-DC conversions, and then DC-DC converters will be used to match the desired voltage level of batteries.
FIG. 1 is a block diagram showing a conventional EV charger unit by CHAdeMo, Technical Specification of Quick Charger for Electric Vehicle, Jan. 31, 2012. As shown in FIG. 1, the EV charger unit 1 includes an AC/DC converter 10 and a DC/DC converter 11 that are linked in series.
An EV charging station may comprise at least one EV charger unit so that it can charge the battery of at least one electrical vehicle. Dependent on the type of the bus bar, the EV charging station can be defined as two types: AC bus based station and DC bus based station. FIGS. 2 and 3 respectively show a conventional AC bus based EV charging station and a conventional DC bus based EV charging station. As shown in FIG. 2, the AC bus based EV charging station 2 includes at least one EV charger unit 20 that is coupled to the AC bus bar 21. The AC-DC converter 200 used in each EV charger unit 20 is called distributed AC/DC converter considering that they are distributed with the EV charger units 20 in the AC bus based EV charging station 2. Description concerning FIGS. 2 and 3 of WO2012/119300 A1 also teaches the AC bus based EV charging station. As shown in FIG. 3, the DC bus based EV charging station 3 includes at least one EV charger unit 30 that share the same AC/DC converter 300 but each of them comprises separate DC/DC converter 301. The input of the DC/DC converter 301 is coupled to the output of the AC/DC converter 300 via a DC bus bar 31. As compared with FIG. 2, in the DC bus based EV charging station, the AC/DC converter 300 is utilized to replace the distributed AC/DC converters 200 and thus it is called central AC/DC converter.
From both AC based and DC based EV charging station solutions, all converters used as EV charger are full-power converter. Take a 50 kW×6 charging station as an example, the total capacity of the converter system is 600 kW which is actually doubled (50 kW×6 for AC/DC stage, 50 kW×6 for DC/DC stage). The full power-converter brings high cost, high losses and large foot print/weight. Besides, to charge EV batteries with different nominal voltage levels, different chargers with various rated voltages should be designed and manufactured separately, which leads to an increased cost on product R&D and manufacture. This also limits the flexibility of EV charger operation. For example, EV chargers designed for electric passenger vehicles cannot be used to charge electric buses. And the efficiency of the chargers for electric buses will decrease if it is used to charge electric passenger vehicles.